"Mechanix Menace": An LS7-motivated, chopped and heavily modified 1973 Datsun 240Z

[chevyz240]

The part of the roll cage cross I had to cut off has been replaced by a new piece of tubing and both diagonals going from the floor up to the cage have been tacked in place. This is the last bit of welding I will do in a while. It's not sensible to continue with the rear part of the chassis before I know exactly at what height and at what angle I will place the rear suspension subframe.

I took the opportunite to tidy up the garage and clean up all the metal shavings and dust. Since I'm not going to cut metal for a while, this seemed like a good time to do it!

The next step is to take the rear suspension to work and use our high end 3D scanner to scan it. After that I will put the geometry in the CAD system and find all suspension pivot points. They will then be entered into a suspension software and there I will experiment with different heights and side view angles to try to find the best compromise between roll center height, camber curves and a multitude of other parameters. Only after that can I design the exact geometry of the rear part of the chassis.









As (almost) always; more pictures at https://www.facebook.com/MechanixMenace

[TANKMASTERJ]

Wow looks like your chassis work is coming along strong Henrik. I'm sure it seems slow to you on your end but I notice the progress . This is such a cool and creative build I love it.

Jason

[chevyz240]

Wow looks like your chassis work is coming along strong Henrik. I'm sure it seems slow to you on your end but I notice the progress . This is such a cool and creative build I love it.

Jason

Thanks Jason! Well, the progress is a lot quicker than in the last few years at least! ;)

[chevyz240]

Not much has happened in a month. I have been practicing using the FaroArm at work that I will use to 3D scan the rear suspension. I have also started dismanling the rear suspension to make the 3D scanning simpler. Yesterday I cleaned some of the parts to be scanned. Hopefully, I can start doing that next week.







This time only one more picture at https://www.facebook.com/MechanixMenace

[chevyz240]

I have started 3D scanning some rear suspension parts. I probably haven't touched on but a small percentage of all the different parameters you can adjust to get a good scan, but it's not as simple and easy as you might imagine. First, it's not easy to see if you have covered the entire surface or if there will be some holes in the scan. Also, some surfaces are difficult to scan, like matt black rubber. You can put different kind of coatings on the part to ease scanning, but in my case it's really not that critical. For the important surfaces, I'm using a mechanical probe. This would really suffice for the info I need to put in my suspension software to check all important suspension parameters, like roll center position, camber curves, etc. But, I still like to have the shape of all the parts, to put in my CAD model, partly to have the ability to check for clearance against the exhaust system and other parts, but mostly because I think it's cool to have the complete suspension scanned in a nice way.

The CAD system at work unfortunately doesn't handle surface models, so I really can't do much editing on the point clouds I get from the scanner. Luckily, the freeware Blender I have been using for the body design can be used to fix things, like mending holes. Even if I scan at the lowest resolution, the point cloud still gets pretty large, so patching up things get pretty tedious, as the mesh has such a fine resolution. Again, this really isn't necessary, but I like things to look good!

To know the articulation point of the ball joints on some of the suspension links, I probed them in a few different positions. I then extended the stud centerlines to see where they merged, that is the articulation point. Due to measurement accuracy and play in the ball joints, they of course don't merge in exactly the same point, but close enough!

Today I have been out mountain biking with a friend, and as I write this, I listen to some old classics, like Buggles and ELO, while working in the CAD system, eating pizza and replenishing the fluid loss with Hefeweizen beer! There are worse ways to spend a Saturday afternoon! (During the MTB trip, I of course had some whiskey to take the fear off from some of the scarier passages! )







As (almost) always; more pictures at https://www.facebook.com/MechanixMenace

[chevyz240]

During the summer, I have been doing a lot of mountain biking, digging dirt and refilling after my basement drainage and insulation work. I have also drank a few beers and some whiskey! Irish (not Scottish), hence the spelling...

Before the summer vacation, I finalized 3D scanning all the rear suspension parts. After that, I cleaned up the individual CAD models so they at least look decent. That takes quite a lot of time.

In order to find the center of ball joints, I probe the stud in four different positions (two is enough, but I want to make sure that play and faulty measurements aren't screwing things up). I then extend the stud centerlines to find the intersection. If they all end up in the same point, there is no play and the measurements are correct. That point is then the center of articulation!

After finding all articulation points and axis on all suspension members, I could then constrain them to each other in the proper way in the CAD assembly.

Previously, I hand measured the entire rear suspension and rough modeled it in the CAD, in order to be able to start on the chassis modeling. Now, I could compare it to the scanned suspension. They came out pretty close! I guess I am getting used to making reasonably accurate measurements!

The next step was to find all the coordinates for the suspension joints. I could then put them in the Shark suspension software. The software has templates for 29 different suspension systems, but unfortunately none for the BMW integral link rear suspension. I had to model it myself. That took a lot of hours! The trickiest part is to specify how the suspension members interact with each other to get the suspension to move in the correct way. If something is wrong, the system crashes and a lot of times you have to start from scratch again! Highly annoying! I almost gave up and thought that this system might not be possible to model, but after a lof of trial and error, I finally succeded! Super nice!

Now I can start experimenting with the position of the suspension to get the roll center, camber, toe and other curves the way I want. One of the biggest problems is deciding which compromises are the best. I have been trying to read up on this a lot over the years, and I have dug into it even more lately. SInce I have decided on not modifying any pickup points on the subframe itself, I have at least reduced the number of variables quite substantially.

I guess I will spend a few weeks tweaking the geometry before fixing it. I then can finalize the design of the back part of the chassis and get back in the garage actually building the car again!







As usual; more pictures (and this time movies) at https://www.facebook.com/MechanixMenace

[chevyz240]

The last weeks I have been working on the rear suspension geometry. Pretty small changes in subframe height impact the roll center height quite a bit. This means that having the correct loaded tire radius and ride height becomes very important. During the years I think I have probably spent over a 1000 hours looking at what tires and rims to use. Basically, it’s impossible to find a combination of looks, rim quality, bolt pattern, offset, rim and tire width, rim and tire diameter, tire quality and some other parameters that I’m looking for without going totally broke!
I think I have decided on using Michelin PS4S tires as a good compromise between road and track focus. The rears I’m planning to use are 305/30-19. There are also quite a few other alternatives in this dimension. I can also find rims with the correct offset and width with looks I like.

For the fronts, things get a lot trickier… I am leaning towards using Corvette C6 or C7 spindles and A-arms for the front suspension. I want to keep the scrub radius low to keep the car from being too nervous on rough roads. That means I need rims with a high offset. Ideally, I would like to use 255/35-18 front tires. I don’t want a tire side wall that is too low, both from a grip and comfort perspective. Unfortunately, I don’t find many rims that fit these demands. If I instead choose 255/30-19 tires, the rim choices open up. I definitely don’t want a front tire sidewall that is taller than the rear, as I think this looks really ugly! Since these two front tire sizes have almost identical diameters, I don’t have to decide right now.

After a lot of thought back and forth, I have decided on 100 mm ride height at the rear wheel center, and 90 mm at the front. This is measured to the underside of the flat floor, so nothing will hang down below. The small rake is due to aerodynamics and looks.

The rim choice will probably change a few times, but right now I’m looking at the Forgestar CF10. I actually like the Apex SM-10 even better, but that’s not available in the front wheel dimensions I need. The OZ Formula HLT is also an option.

There is a high likelihood I will have to redrill the wheel hubs for a new bolt pattern, remachine the wheel center bores and use spacers in the end. I will know in the distant future…

With the ride height, rear tire and rim specs set, I could finalize the rear geometry. Compared to stock, I have lowered the roll center, since it gives a better camber curve and I also think with my lower CG and good shock absorbers this is a good roll center height. I also decided to keep the side view angle of the suspension stock, as I don’t see any benefits changing it. This meant that I could now modify my chassis model to fit the position of the rear suspension.

Previously, I used my manual suspension measurements and some guesswork on where the suspension would be positioned. With the scanned suspension and my decisions above, the rear part of the chassis needed to sit a bit higher up. This weekend I have spent many hours modifying the chassis model. It is far from finished yet, but now I have at least gotten the tubes that the subframe attaches to in position.

Maybe next weekend I can crawl back into the garage and start cutting and welding tubes again!







As usual; more pictures at https://www.facebook.com/MechanixMenace

[TANKMASTERJ]

Henrik, Well, this is more and more impressive as time goes on. You have the patience of Job. Man love this car cannot wait to see it rolling.
Jason

[chevyz240]

Henrik, Well, this is more and more impressive as time goes on. You have the patience of Job. Man love this car cannot wait to see it rolling.
Jason

Thank you very much Jason!

I repeatedly question my sanity... I almost wish I didn't have this need to go into detail on everything and have the need for every little bit being exactly as I want. Things would be a lot easier and quicker if good enough would do it for me. Around 10 years ago, I was maybe a month's work away from being able to take the first test drive with the LS7 installed. Then I decided to build the tube chassis...

It really is a life-long project. The reason I bought the car was for it to be a substitute for my tube chassis, twin turbo, chopped Volvo Amazon project that had snowballed. (Maybe you've seen it at the beginning of this thread.) This was in 1988...

Maybe 10 years ago I used to joke that the car would be finished when I retire. That's not gonna happen... Retirement is only three and half years away. I hope I at least can take a test drive before then.

[chevyz240]

This is not a post about the Z-car project, but this kind of explains the road that finally led me to start building the Z!

My first car project(s)!

When I was 18 (this is the age you need to get a driver’s license in Sweden) , in January 1980, I bought a 1966 Volvo Amazon station wagon. Just a few days after the purchase, I started to tear the car down to a bare body. My initial plans were to make it into a pickup truck, with a chopped roof. At that time I was reading Truckin´ Magazine. When I started to fix some rust I noticed that the front end had some crash damage and was slightly warped. I tried to fix this by heating the sheet metal and putting a wheelbarrow full of heavy objects on a long steel bar attached to the front end to try to twist it back into shape. I think I got it halfway decent. In that period Corvette L88 scoops were popular to put on all sorts of cars. Of course I had to have one myself! Since I have never been content with anything as is, I had to modify it further. The plan was to add a couple of small scoops on top of it.

When I had cut the rear half of the roof off and had started chopping the front part, I changed my mind, now wanting to build a chopped delivery truck instead. I went to a junkyard and cut off another station wagon roof and started the new modifications. After a while I changed my mind again, partly because the body still was a bit warped; I now wanted to chop an Amazon sedan instead. So, in October the same year I bought one (also a -66) from a class-mate. The station wagon was scrapped and I started working on the sedan instead.

The initial plans were to chop the car, install a turbocharged Volvo B20 4-cylinder engine and modify the stock suspension. I wanted sleek lines, so instead of lengthening and widening the roof, I tilted the roof pillars in instead. The chop itself was 8 cm (3”). The windshield wasn’t laid back, but the rear window was laid down quite a bit. When most people do this, they don’t change the shape of the roof, meaning there will be a kink between the roof and the window. This was not acceptable to me, so I sliced off a little bit of the rear part of the roof, moving the upper window frame forward, creating a smooth transition between roof and rear window. Of course the drip rails were shaved too!

I also rounded all window corners and changed the shape of the quarter window frames to have the same design as on the doors and to line up the window edges. The stock quarter windows have a chrome frame which doesn’t match the look of the door windows, nor do the edges line up between door and quarter windows. See the picture of the stock red Amazon. (This is another car I had which I repaired rust on and then painted. I then crashed it shortly afterwards doing some spirited driving…)

The windshield was a cut down stock windshield. It took three attempt for the glass guy before he got one that didn’t crack. The side windows were custom flat hardened glass. Since the rear window now had a different curvature and bigger size, it was made from thick Plexiglas. All windows were ordered in the same bronze tint. I built a wooden buck with the correct shape which was covered in felt. I then laid the Plexiglas on this and put it in a big oven we had at work and it baked in 190 degrees C (374 deg F) for several hours. The result was a window that was pretty close to the correct shape.

I wanted to change the look of the front end of the car, and I did some quite extensive modifications there; the hood bulge was sectioned to make it sleeker, I changed the shape of the grill opening (I was inspired by Chevy -55 pickups and maybe the Chrysler 300 -57). I also frenched the headlights and molded on some eyebrows inspired by -55 Chevy passenger cars. The bumper was seam welded and molded in. The turn signal lights were changed to bullet shape lights, which were also frenched. After bodyworking everything I then pulled a mold from this and made a tilt front end in fiberglass.

In 1982 new registration rules were introduced allowing home built and heavily modified cars to be registered for road use. Between 1969 and 1982 this was basically not allowed. At the same time a guy living two blocks away came out with his chopped Amazon with a supercharged Volvo B20. Suddenly, my car wasn’t as unique and cool anymore… Due to this, I decided to build a full tube frame for the car and register it as an “amateur built vehicle”. I cut away the stock engine compartment and floor that I had spent quite some time scraping undercoating from. I built a chassis jig based on two railroad rails that I stole from a scrap metal yard! They were around five meters (16 ft) long and weighed around 250 kilos (550 lbs) each. I transported them one by one in my Amazon station wagon (another one). A friend had to sit on the front end of the rail to prevent it from tipping over backwards. The rail stuck out around two meters (7 ft) out of the car and the steering got really light!

In order to build the tube frame, I had to have a tubing bender. I built this myself at work (I was working as a tool maker and machinist during summer vacations and sabbatical years when studying) using a 10 ton hydraulic jack as a base. The tube frame was constructed from round and square mild steel tubing. The parts that aren’t triangulated in the pictures were meant to have aluminum sheets glued and riveted on both sides of the tubing to create stiff boxes. At this point I also decided on sectioning the body to make the car even lower. Well, to be correct, I actually was going to cut away the rocker panels to make the body lower.

I was using a Chrysler 8 ¾” rear axle hung in a four link and a Watt’s linkage. The front end was a double A-arm design using Jaguar spindles that I had bought. I created a computer program in BASIC (I think it was around 300 lines of code) to optimize the front suspension geometry. I ran this on my father’s Commodore 64 or 128 computer. I remember that a single run took around 15 minutes and I made maybe 50-100 runs! The intention was to have a car with really good handling. At one point I planned on using 16” wide rear tires! The engine I was going to use first was a 327 Chevy small block that I had bought. Later I changed that plan to a twin turbo 350 that I ran briefly in a -62 Nova. This was in 1987. At that time there were very few turbo V8’s in Sweden. The transmission was a Muncie M22 that I bought during a two month road trip in the USA that I made with a friend after graduating from KTH Royal Institute of Technology in 1987.

The project snowballed and it really hurt not having a cool car to drive in the summer. This led to me buying some other cars that were only meant as substitutes while continuing the work on the Amazon. Naturally, I couldn’t keep my hands away from them either, so I ended up doing a lot of work on them too, further delaying the Volvo project. Those cars were a -70 Dodge Dart GT with a 360, a -70 Plymouth Duster that I put a 440 and Hemi four speed in. That engine and transmission came from a -67 Plymouth Belvedere station wagon that I bought and then sold as a rolling chassis. The final substitute car I bought was my -73 Datsun 240Z that I bought in December 1988. I ran it in stock condition in the summer of -89, using it as my daily driver. I also went on a road trip to Paris in it with a friend that summer. We did a lap on the Nürburgring too!

The intention was always to finish the Amazon project, but I knew it would take a few years before it was done. I had seen that it was popular to put Chevy small blocks in Z-cars in the USA, and since the engine compartment is quite big, I thought that I would put the 350 in it over the winter, so the car was even sportier and more fun to drive the next summer. After that I would continue with the Volvo… Due to me being an extreme time optimist, a couple of job changes and living in Germany a year, the Z wasn’t back on the road again until -96. I now started to think that maybe I should continue modifying the Datsun instead and sell the Volvo project.

After mulling it over for a few years, I sold the Volvo chassis in 2000 to a guy that was going to use it in a BMW E30. The Volvo was going to be 112 cm (47”) high and the Bimmer is probably around 20 cm (8”) taller, so I don’t really know what he was thinking… The body was sold in -03 to a guy who had a chopped Amazon and was going to use mine as a caravan to tow behind his car! Also quite interesting! I guess you could but a twin bed in it, but hardly any chairs or a table. Well, at least I got it sold at last. I talked to the guy a couple of years ago and he said that he had cut the body in half and had widened it 15 cm (6”), but that nothing more had happened. I checked recently and he is still the registered owner. At some point I think I will visit him to check the car out for nostalgic reasons!

Basically you can say that the reason I am building my Z-car is that the Amazon project snowballed! Now the Z-car project also has snowballed and it has spawned a few substitute car purchases as well! Many years ago I said that the Z would be done when I retire. I said this as a joke. I am planning to retire in three and a half years; that sentence is no joke anymore… I hope I at least have taken a test drive with it then, even if it’s not fully finished. We will see…









As usual; more pictures at https://www.facebook.com/MechanixMenace

[andrewb70]

Very cool. Tha is for sharing the story!

Andrew

[chevyz240]

Very cool. Tha is for sharing the story!

Andrew

Thanks Andrew! I thought it could be a bit interesting!

[chevyz240]

As you guys know, I have been thinking about making the entire car body, except for the roof, out of fiberglass. The reason is that I would like to widen the entire body, instead of just slapping on some big fender flares. When I bought my 3D printers, the idea became much more viable, since I can create a buck from 3D printed pieces. I have waited to make the decision, as I tend to downplay how much extra work my choices sometimes create. Well, now the decision has been taken, and there is no turning back!

This Friday, I started preparing for the rear chassis jig I will build. The welding accessibility to everything would be so much better if the rear part of the body was gone. I slept on it, and yesterday I took the plunge and simply cut it off! Before doing that. I measured some points on the quarter panels and suspension cross members to see if there would be any distortion after the cut. Everything stayed within a millimeter, so that was OK.

One reason that it was easier to make the decision to make a fiberglass body is that the car has been crashed and repaired and there is quite a bit of bondo on the body. If the sheet metal was nice and straight, it would have been a harder decision to make. Later on, I will cut away the rest of the quarter panels and probably the door jambs as well. I will only leave the quarter window frames, where the fiberglass body will be attached.

Now I can start modeling the car exactly as I would like it to look! I will try to keep many of the Z-car features and have quite a bit of OEM feel to it. It shouldn't be obvious exactly how the proportions have been changed. This will be fun!

One thing that I would like to find is a software that can analyze surfaces and say if something is off regarding curvatures and how different shapes interact. Basically, I want to know if there are shapes that look like they have dents or bulges and if some lines look strange from any perspective. I am quite positive that this is something the OEMs have, but if someone can point me to a software that's available at a reasonable price, please let me know! Or if there are companies that offer the service.

Now it's time to go out for a morning mountainbike ride in the cold, grey December weather!

Over and out!







As usual; more pictures at https://www.facebook.com/MechanixMenace

[chevyz240]

I have created the part of the chassis jig that will locate all the tubes for the rear suspension. When leveling the particle board, I noted that my spirit level had lost it's calibration. I did a new calibration, which took some time; first I needed to create a flat surface. I did that by taping a couple of wood blocks on to a workbench. I then put the level on to those blocks and checked the position of the bubble with the level turned one way and then the other. I put pieces of tape on to the low block until the bubble was roughly in the opposite position when the level was turned 180 degrees.

I then started to adjust the vial. After getting that fairly correct, I fine adjusted the height of the wood blocks. I could then fine tune the vial. Since the vial can move out of position when tightening the screws, this takes several attempts. Finally, I had it close to perfect. This is an old level I have inherited from my father and it is super accurate. With some practice, you can see if the surface is out of level with 0.1 millimeter per meter (0.0012 inch per foot). This is equal to 0.006 degrees. I have not been able to find new levels with that accuracy. My fairly expensive digital level can show 0.05 degrees.

After building the jig and adjusting the height and angle of the build surface, which also took quite some time, I created a centerline, using the centerline I have on the garage floor. Then I marked out a length reference line and created a transverse line that is exactly 90 degrees from the centerline. From these lines, I could then mark out the lines for the three square tubes that will be the base of the rear part of the chassis.

Maybe I can start welding stuff again next weekend!







As usual; more pictures at https://www.facebook.com/MechanixMenace

[Motown 454]

Looking good! Every time I check in The work your doing amazes me.

[chevyz240]

Looking good! Every time I check in The work your doing amazes me.

Thank you very much Wayne! It's always inspiring to get some positive feedback!

[Motown 454]

You definitely earned it!

[chevyz240]

You definitely earned it!

Thanks again!

[chevyz240]

This week I have prepared and tack welded the three square tubes that form the base of the rear part of the chassis. The rear subframe will be bolted to these tubes (basically). I have previously praised my 3D printers when making notching templates. This time the job would have been even trickier than normal without this method, since there are two oddly shaped notches at the front of the two longitudinal tubes.

I first 3D printed replicas of the front part of those tubes, to see what needed to be corrected compared to the CAD model. Since there is a tolerance chain deciding the spacing between the transverse tube and the diagonal tubes, they weren't 100% according to the CAD model. I could then make some slight corrections to the CAD model and 3D print notching templates in the normal manner. In the end I got the fit pretty nice!

Now I need to start thinking about maybe fully welding some joints before adding more tubing in order to try to minimize distortion of tubes that matter the most.







Many more pictures at https://www.facebook.com/MechanixMenace

[chevyz240]

I have seam welded the tubes going to the top part of the "rear suspension towers". Due to old age, unergonomic working positions and lack of practice lately, they aren't the nicest of welds, but I think they will do from a strength perspective. I have also made the fixture for the tubes connecting the suspension towers to the "subframe tubes". Today I came a bit on the way of cutting those tubes to size. That basically wraps up 2022! Lets's hope 2023 brings a lot of progress!







As usual; more pictures at https://www.facebook.com/MechanixMenace